1. Field of the Invention
The present invention relates to a heater device for motor vehicles, and more particularly to an automotive heater device having a heating circuit combined with an engine cooling water circulation circuit and incorporating a combustion heater.
2. Prior Art
Japanese Patent Laid-open Publication No. 62-12411 discloses a heater device for motor vehicles of the type which includes a circulation circuit for circulating engine cooling water through a heater core disposed in the passenger compartment of a motor vehicle, and a combustion heating circuit combined with the circulation circuit for heating the engine cooling water by a combustion heater.
The supply of engine cooling water to the combustion heating circuit is controlled by a directional control valve with four ports and four distinct directions in the manner described below. An engine needs a relatively long warming-up when started in a cold area. In this instance, the engine cooling water is circulated exclusively between the combustion heating circuit and the heater core to thereby elevate the temperature of the passenger compartment rapidly Such circulation of engine cooling water is also performed when an occupant of the passenger compartment takes a nap while the engine is being stopped, thereby saving the overall fuel consumption.
While the engine is operating at a predetermined temperature, the supply of engine cooling water to the combustion heating circuit is interrupted and the engine cooling water is supplied directly to the heater core.
The directional control valve incorporated in the known automotive heater device includes, as reillustrated here in FIG. 8, a second discharge conduit A for supplying the engine cooling water to the combustion heater, a second intake conduit B for receiving the engine cooling water flowing from an engine radiator, a first discharge conduit C for supplying the engine cooling water to the engine radiator, and a first intake conduit D for receiving the engine cooling water from the engine, the conduits A-D being arranged in the order named and angularly spaced at equal intervals. The directional control valve includes a rotary spool F having an arcuate internal hole E.. The arcuate hole E serves to interconnect two adjacent conduits A-D for changing the path of circulation of the engine cooling water. For example, when the first intake conduit D and the second discharge conduit A are connected together, the engine cooling water is circulated successively through the engine, the combustion heater and the engine radiator. Likewise, when the second discharge conduit A is brought into fluid communication with the second intake conduit B, the engine cooling water is circulated exclusively between the combustion heater and the engine radiator. Yet, the engine cooling water is circulated exclusively between the engine and the engine radiator when the first intake conduit D and the first discharge conduit C are connected together.
The known heater device having such directional control valve is disadvantageous in that the arcuate connecting hole or passage E in the rotary spool F has a greater flow resistance than a straight passage and hence tends to lower the flow quantity of engine cooling water flowing therethrough. With this reduced flow quantity, the heating ability or power of the known heater device is relatively low.